1. Field of the Invention
The present disclosure relates to an array substrate for an organic electroluminescent display device, and more particularly, to an array substrate for an organic electroluminescent display device that includes a polycrystalline silicon thin film transistor and a method of fabricating the same.
2. Discussion of the Related Art
With rapid development of information technologies, display devices for displaying a large amount of information have been promptly developed. Recently, flat panel display (FPD) devices having a thin profile, light weight and low power consumption have been suggested and actively pursued.
Among these, organic electroluminescent display devices have been recently spotlighted because they have many merits as follows: organic electroluminescent display devices have high brightness and low driving voltages; because they are self-luminous, the organic electroluminescent display devices have excellent contrast ratios and ultra thin thicknesses; the organic electroluminescent display devices have response time of several micro seconds, and there are advantages in displaying moving images; the organic electroluminescent display devices have wide viewing angles and are stable under low temperatures; since the organic electroluminescent display devices are driven by low voltage of direct current (DC) 5V to 15V, it is easy to design and manufacture driving circuits; and a manufacturing process of an organic electroluminescent display device is very simple because substantially only deposition and encapsulation apparatus is required. In the organic electroluminescent display devices, active matrix type display devices have been widely
An organic electroluminescent display device includes an array substrate on which thin film transistors for turning on/off respective pixel regions are formed. Thin film transistors may have polycrystalline silicon as a semiconductor layer. An array substrate for an organic electroluminescent display device including polycrystalline silicon thin film transistors, generally, is fabricated through 9 or 10 mask processes.
After forming a material layer on a substrate, a mask process includes steps of forming a photoresist layer on the material layer, exposing the photoresist layer to light through a photo mask, developing the light-exposed photoresist layer to form a photoresist pattern, etching the material layer using the photoresist pattern as a mask, and stripping the photoresist pattern.
Therefore, to perform one mask process, apparatus and materials for each step are needed, and time for each step is also required. In manufacturing an organic electroluminescent display device, trials and efforts for reducing the mask processes have been made.
Meanwhile, in an organic electroluminescent display device including polycrystalline silicon thin film transistors, a storage capacitor having a large capacitance has been requested at each pixel region for stability in displaying images.
By the way, as the display device has high resolution, a size of the pixel region decreases, and the capacitance of the storage capacitor is lowered due to a decreased area of electrodes of the storage capacitor. To increase the capacitance of the storage capacitor, the area of the electrodes of the storage capacitor may be increased, and the aperture ratio of the display device may be decreased.